CHARACTERIZATION OF THE INTERFACIAL BOND IN PAPER-POLYPROPYLENE LAMINATES AND THE EFFECTS OF AGING UNDER SERVICE CONDITIONS

This study focused on the behavior of the paper-polypropylene-paper (P PP) laminate while aging in hot oil in the absence of voltage stress. The results provide an understanding of both the quality of the interf acial bond and the performance of this bond during service. X-ray phot oelectron spectroscopy performed on two different peeled laminates sug gest that the bond failed primarily adhesively. Weibull statistical an alysis of the peel strength data obtained on unaged laminates and thos e aged in polybutene oil at 90 degrees C for 120 hours showed that the strength loss is consistent with one failure mechanism and the failur e rate increases with applied stress. For the aged sample, Weibull ana lysis results are consistent with the prior loss of peel strength due to the aging. Experiments on the solubility of the oil show that lamin ation reduces the amount of absorption in comparison to the unlaminate d composite. Swelling experiments on the individual components show di fferential swelling between the paper and polypropylene to be the sour ce of the strength loss. The polypropylene swells, and the paper shrin ks. Measurements on the laminated show that both paper and polypropyle ne shrink, indicating that the paper governs the laminate swelling pro cess. During aging, the differential swelling generates internal stres ses on the interface. In addition to yielding the magnitudes of these stresses, finite element analysis also predicts plastic deformation an d creeping of the polypropylene as well as tensile stresses between th e paper and polypropylene at a free edge. Very likely these processes damage the bond and contribute to the loss of bond strength.